1. Field of the Invention
The present invention generally relates to an oil activated fuel injector and, more particularly, to a valve control body used with an oil activated electronically or mechanically controlled fuel injector having a spool head which reduces shot to shot fuel variations and other injector inefficiencies.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In conventional fuel injectors, a driver first delivers a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as xe2x80x9cgroovesxe2x80x9d) of the control valve body and the spool. During this shifting of the spool, the spool impacts against the open coil solenoid thus causing a bounding the spool head, itself, against the open coil solenoid. This is especially true at high spool speeds. This spool bouncing may lead to high shot to shot fuel variation and non-linear behavior of the injection quantities at low open coil activation times. This problem appears to be especially acute during the injection of pilot quantities of fuel.
Once there is an alignment of the grooves, the working fluid flows into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure plunger chamber. As the pressure in the high pressure plunger chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
To end the injection cycle, the driver delivers a current or voltage to a closed side of a closed coil solenoid. The magnetic force generated in the closed coil solenoid then shifts the spool into the closed or start position which, in turn, closes the working ports of the control valve body. The working fluid pressure will then drop in the intensifier and high-pressure chamber such that the needle spring will shift the needle to the closed position. The nozzle tip, at this time, will close the injection holes and end the fuel injection process. At this stage, the working fluid is then vented from the fuel injector via vent holes surrounding the control valve body.
The present invention is directed to overcoming one or more of the problems as set forth above.
In a first aspect of the present invention, a control valve body is provided for use with a fuel injector. The control valve body includes an inlet area and working ports. A spool has at least one communication port which provides fluid communication between the inlet area and the working ports. At least one fluid passage within the spool provides fluid communication between the at least one of the working ports and a gap formed between the spool and a coil which is adapted to shift the spool.
In another aspect of the present invention, an oil inlet area and at least one port in fluid communication with the oil inlet area is provided. The at least one port is adapted for transporting oil between the oil inlet area and an intensifier chamber of the fuel injector. An aperture having at least one communication port is positioned about a surface of the aperture which provides a flow path for the oil between the at least one port and the oil inlet area. A spool is positioned within the aperture and slidable between a first position and a second position, and includes at least one communication port which is in alignment with the at least one communication port of the aperture when the spool is in the first position. First and second coils are also provided. At least one fluid passage is provided in the spool and a dampening groove is positioned at the second end of the spool in fluid contact with the oil within the gap.
In still another aspect of the present invention, a spool is provided with a shaft having a first end and a second end, and a dampening groove at one of the ends. A fluid communication path is provided about a portion of the shaft, and at least one longitudinal bore is provided throughout the shaft. At least one hole is in fluid communication with the at least one longitudinal bore.
In also another aspect of the present invention, an oil activated fuel injector is provided. The injector includes a valve control body which has (i) an oil inlet area, (ii) at least one port, (iii) an aperture having at least one communication port positioned about a surface of the aperture and (iv) a spool slidable between a first position and a second position. The spool includes at least one communication port and at least one fluid passage providing a fluid passage for the oil between the port and a gap formed between the spool and a coil. The spool also includes a dampening groove. The injector further includes an intensifier body mounted to the valve control body, a piston slidably positioned within centrally located bore of the intensifier body and a plunger. An intensifier spring surrounds the shaft of the plunger and is further positioned between the piston and a shoulder of the intensifier body. A high pressure fuel chamber is formed at the second end of the plunger and a nozzle is in fluid communication with the high pressure chamber. A needle is positioned within the nozzle, and a fuel chamber surrounds the needle and in fluid communication with the fuel bore.